Adenovirus-mediated intratumoral lymphotactin gene transfer potentiates the antibody-targeted superantigen therapy of cancer.

Bacterial superantigens are extremely potent activators of murine and human T lymphocytes. To engineer superantigens for cancer immunotherapy, staphylococcal enterotoxin A (SEA) was genetically fused to the Fab region of the human colon carcinoma-reactive monoclonal antibody (mAb) C215. Fusion protein C215Fab-SEA can trigger cytotoxic T cells against C215 antigen positive tumor cells and induce tumor-suppressive cytokines. However, the antitumor effect of C215Fab-SEA is often not satisfactory because of T cell deletion after activation and failure to induce potent CTL activity after repeated administration. Lymphotactin (Lptn) is a potent chemoattractant for T cells and NK cells. To improve the therapeutic efficacy of fusion protein C215Fab-SEA we investigated in this study the antitumor responses elicited by combination of C215Fab-SEA and adenovirus-mediated intratumoral Lptn gene transfer in the preestablished C215 antigen expressing B16 melanoma murine model. More significant inhibition of tumor growth and prolonged survival time were observed in tumor-bearing mice that received combined therapy of C215Fab-SEA and Ad-Lptn than those of mice treated with C215Fab-SEA or Ad-Lptn alone. The highest CTL activity of tumor-bearing mice was induced after combined therapy. Intratumoral coadministration of C215Fab-SEA and Ad-Lptn augmented splenic NK activity of tumor-bearing mice most markedly. Our data demonstrate that the in vivo antitumor effect of C215Fab-SEA immunotherapy is potentiated significantly by combination with intratumoral Lptn gene transfer through more efficient induction of specific and nonspecific antitumor immune responses.